Advanced Aggregation in MongoDB - Examples and Best Practices

Create a Sales Summary Pipeline

Build an aggregation pipeline that calculates total sales, average sales per category, and lists top 3 customers by sales amount.

Expected output: A single aggregation result with total sales, average sales by category, and top customers.

Hint: Use $group, $sort, $limit, and $facet stages.

Join Collections with $lookup

Write an aggregation pipeline to join a products collection with reviews, including average rating per product.

Expected output: Documents with product details and average review ratings.

Hint: Use $lookup to join and $group to calculate averages.

An aggregation pipeline is a sequence of stages that process documents in a collection, transforming and aggregating data step-by-step.

$lookup performs a left outer join between two collections, embedding matching documents from the foreign collection into the results.

$facet is used to run multiple aggregation pipelines in parallel on the same input documents, useful for generating multiple reports in one query.